BAGHDAD — A suicide car bomber crashed his vehicle into a barrier outside a police building in central Iraq on Thursday, killing 20 policemen and wounding dozens more, an official said.

The blast is the second significant attack in Iraq since the death of Osama bin Laden Monday at the hands of a U.S. commando team in Pakistan. Iraqis have been on edge, waiting for al-Qaida's branch in Iraq to strike back as a way to demonstrate it is still dangerous.

Iraqi security officials have said they are increasing security in the wake of bin Laden's killing. Already security is vastly improved since the days when bin Laden's associates terrorized the country, but Thursday's deadly attack against security forces underscored how difficult it is for Iraq to wipe out all traces of the insurgency.

A police official said the bomber hit when the officers were assembling in a square in front of the police building for a shift change in the city of Hillah, about 60 miles south of the capital Baghdad.

A member of the Hillah city council, Mahmoud al-Murshidi, who spoke to The Associated Press from the hospital, said 20 were killed and 43 people were wounded in the bombing. He said all the casualties were policemen.

A witness at the scene said the blast knocked down the concrete ceiling covering a parking lot where many police cars were located.

Other buildings on the main road, including shops and houses, were also damaged.

"The negligence comes from Baghdad because we're always asking them to increase the number of our policemen, but there is no response," Kadhim Majeed Tuman, the head of the Babil provincial council, told Reuters.

Haidor Zambor, head of Babil province's security committee, placed the blame on al-Qaida. "This was a breach of our security by al-Qaida," he said according to The New York Times.

"We were expecting that Babil would be the target of revenge for the killing of bin Laden. We will increase the security procedure to prevent this from happening again.

Triangle of Death
The fact that the bomber was able to wipe out so many policemen in one blast immediately raised questions about security at the building.

"The incident is definitely a security breach and all the security services in the province, especially the police command, are held responsible for that," said Mansour al-Mani'i, another member of the Hillah council.

Hillah is a predominantly Shiite city but its proximity to the Triangle of Death — a mainly Sunni area that at one time was one of the most dangerous in the country — has made it a frequent target of Sunni extremists.

There was no immediate claim of responsibility for Thursday's blast, but extremists like al-Qaida in Iraq have often tried to take out Iraqi forces as a way to undermine security in the country.

On Tuesday, a car bomb tore through a cafe in Baghdad packed with young men watching a soccer match on TV, killing at least 16 people.

Most of the dead and wounded in the cafe were young people. The blast occurred in a Shiite enclave in the former insurgent stronghold of Dora, an area in southwestern Baghdad that saw some of the fiercest fighting of the Iraq conflict.

Nobody has claimed responsibility for that attack either, but Sunni insurgents have often targeted Shiites, who they don't consider to be true Muslims, as a way to incite sectarian violence.